No abstract

On the basis of radial-axial rolling of ring billets, resource-saving technologies for metal forming have been created. Determining the rational parameters of this process is the actual scientific and technical task at development of new profiles. The method of three-dimensional finite element modeling is the most effective tool for improving the technological conditions of ring rolling process. However, as practice has shown, the finite element modeling method requires adaptation to each process of metal forming. This is the subject of the present work. The expediency of using dependency for calculating the metal flow stress for finite-element modeling of ring-rolling processes is substantiated. This dependence was developed on the basis of a theory that takes into account the chemical composition of structural carbon steel, its temperature, strain rate, accumulated deformation, and also the processes of dynamic transformation of the metal structure during hot rolling. A computer program for automated determination of dependency parameters has been developed. The analysis of the accuracy of the obtained dependence was performed in relation to the experimental data. In the course of these calculations, the method of automated determination of the metal flow stress was used by spline interpolation of the experimental data included in the computer database of digital information for a particular steel grade. The average relative error of calculated values of the metal flow stress was 8 % relative to the experimental ones. An improved method is proposed for calculating the parameters of ring billets rolling and reaching the required growth rate of the ring diameter implemented in a finite element modeling system, which is similar to the way the control system of the ring-rolling mill works in solving the same problem (reaching the required growth rate of the ring diameter) when implemented appropriate rolling in practice. When calculating the size of the compression, the iterative process and the method of half division were used. The average deviations of calculated values of the parameters of ring billets rolling from the experimental did not exceed 12.4 %, which makes it possible to apply the proposed approach to study the patterns of the rings rolling process and to improve the rolling technology.

The work is devoted to development of a method for accounting residual technological stresses in wheel disks, which will provide both the versatility of the approach and the accuracy of calculations. The analysis of stresses in the wheel disk from the action of assembly (interference between the hub and the axle) and operational loads is carried out on basis of the results of finite element modeling. Verification of adequacy of the used model was made by comparing the calculated information with the experimental data of JSC “VNIIZHT”. The analysis of calculated and experimental values of radial stresses was carried out for the most loaded (critical) zones of the disk during operation – the zones of its interface with the rim and the hub. It was found that by setting the interference fit value to be greater than the actual one, it is possible to obtain the formation of additional stresses in the wheel, which, with a sufficient degree of accuracy, reflect the effect of residual technological stresses on its stress-strain state. On the example of calculating a wheel with a flat-conical disk (GOST 10791 – 2011), it is shown that an increase in the interference fit value by 60 % (from 0.25 mm to 0.4 mm per diameter) makes it possible to adequately predict the magnitude of stresses in the most critical disk elements. The maximum relative deviations of the calculated values of radial stresses from the experimental ones, both along the outer and inner sides of the wheel, do not exceed 14 %. Despite the simplicity of implementation, the proposed method provides an increase in the accuracy of predicting the strength characteristics of wheels, as well as the possibility of using it for various standard wheel sizes.

The actual problem of increasing the service life of stamped-rolled railway wheels is a complex problem. Residual technological stresses, which cannot be completely eliminated, have a significant effect on the stress-strain state of the wheel as a whole and its disk in particular. At different stages of roughing wheels machining, the residual stress field is continuously changing. This makes it difficult to take into account the residual stresses in the wheels strength calculations. In Report 1 of this work, an accounting method for residual technological stresses was proposed, the essence of which is to set the value of interference between hub and axle when modeling is greater than the actual one. This approach made it possible to obtain additional stresses in the wheel, which adequately reflect the effect of residual technological stresses. In this part of the work, the authors have carried out practical implementation of the developed method and assessment of the degree of residual technological stresses influence on stress-strain state of the wheel disk under the action of operational loads. With regard to the design of a 957 mm diameter wheel with a flat-conical disk (GOST 10791 – 2011), calculations of stress-strain state of the disk under the action of mechanical types of load have been performed. The 60 % increase in the interference between hub and axle realized in the calculations made it possible to establish that the presence of residual technological stresses in the wheel causes an increase of 5 – 38 % in maximum equivalent stresses in the disk zones most loaded during operation. Thus, the proposed method for residual technological stresses accounting allows obtaining an upper estimate of the wheels strength characteristics, and, therefore, more adequately predicting their service life.

The characteristics of finite-element modeling of deformation of billets of railway wheels are considered. On the basis of the performed theoretical and experimental researches, the influence of the basic parameters of the finite-element models on the accuracy of the calculation of the metal forming and forces in the rolling and stamping wheels billet was established. The research included an analysis of power and speed parameters of stamping and rolling wheels billet on the basis of experimental data. Also work on the finite-element modeling of processes stamping between smooth plates, stamping by punch, forming at rolling dies and wheels billet rolling were carried out. It is shown that when creating the models making simplification of the problem can lead to significant distortions of the calculation results, making them unsuitable for practical use.